1. Field of the Invention
The present invention relates to improvements in starters for internal combustion engines, and in particular to the structure of a gear train assembly which couples a drive motor to a drive pinion in a compact arrangement.
2. Description of the Prior Art
An internal combustion engine is generally started by rotating its flywheel until the engine fires and continues to run under its own power. The flywheel is usually rotated by an electric starter motor energized by current from a storage battery. Gasoline engines must be started at a speed of 50 to 60 RPM; diesel engines generally require about 100 RPM. The shaft of the starter is provided with a pinion (a small gear wheel) which, on commencement of the starting operation is shifted forward until it engages the toothed rim on the flywheel. The drive motor of the starter then rotates the flywheel. When the engine has started, the starter pinion is disengaged from the flywheel and retracted. The various types of starters which are in present day use differ mainly in the manner in which engagement and disengagement is effected.
Electric starter motors generally fall under two categories: (a) pinion shift starters and (b) inertia gear drive starters (Bendix type). In the pinion shift starter, when the starter is actuated, the connection between the storage battery and a solenoid switch is established. A powerful magnetic field is set up in the magnetic coil of the switch, which causes the armature to be drawn, slowly rotating, into the magnetic field to engage the toothed rim of the flywheel. In the inertia gear drive starter arrangement, the pinion is shifted along the armature shaft on a quick-screw thread. When the starter button is actuated, the armature of the solenoid switch is attracted and the pinion is pushed forward, while it rotates, by an engaging lever. As the armature of the starter begins to rotate, it advances the pinion until it engages the gear rim on the flywheel. The solenoid switch is held in position by a holding coil, whereupon the electric starter motor can turn the engine.
A common feature of both types of electrical starters is the elongated configuration in which the armature of the starter motor is mechanically coupled in tandem with the pinion shaft thereby producing an unusually long assembly. Additionally, the solenoid switch is usually mounted in parallel with the armature structure and its position relative to the armature it is fixed and cannot be adjusted. The solenoid engaging lever of the electrical drive starters also occupies a substantial amount of space and cannot be moved relative to starter assembly to accomodate mounting variations on the engine to which the assembly is attached.
Although improvements have been made to the conventional electric starter to further reduce its length and overall mounting diameter, there are many applications in which the electric starters cannot be used or are unsuitable for other reasons. For example, most internal combustion engines have at least some difficulty in starting when they are cold. When they are exceptionally cold, as when exposed to extremely low ambient temperature, the difficulty is further compounded. Some engines are exposed to extreme weather conditions and are left unused for long periods of time. Under such conditions, it is sometimes necessary to rotate the flywheel continuously for a long period of time in order to start the engine. It will be appreciated that electric drive motors are not well suited for such extended starting operations because of the risk of overheat and burn-out of the armature due to the heavy current loads required. A distinctly different class of starters, the air motor, is especially well adapted for such starter applications since the air motor can generate a large amount of power in a small frame size and there is no reduction of its power output at low temperatures as there would be with battery operated electric starters. Further, since compressed air is used as the source of power for an air starter, it can produce the required starting torque continuously without risk of overheating. Additionally, for remote applications such as oil production operations, compressed air or hydraulic power may be available, while electric power would not be available. The air starter also has a weight advantage since the heavy batteries are not required.
Although the conventional air start motors perform extremely well under hard start, cold weather conditions, conventional units which are presently available have an elongated configuration in which the drive pinion is coupled in direct axial alignment with the rotor of the air start motor, or is coupled in axially offset, tandem relation with the starter motor by a gear assembly. In either configuration, the overall length makes the assembly incompatible as a universal starter for various sizes of gasoline and diesel engines. Usually, only a limited amount of space is provided adjacent the flywheel housing for mounting the starter motor. The axial and radial clearances of the mounting space is sometimes limited by external engine components and parts such as wiring, fuel lines, mounting brackets and the like. Therefore, for some installations, the available mounting space will only accept a starter motor having a compact overall size, such as an electrical starting motor. However, as previously pointed out, for some applications it is desirable to use an air start motor instead of an electrical motor. Because the length of the air motor and the length of the pinion drive are determined substantially by the horsepower rating, a further reduction in overall length for the extended, tandem air start motor arrangement cannot be expected.